Phonograph pickup



Aug. 15, 1950 J. A. BURTCH PHONOGRAPH PICKUP Filed Oct. 30, 1947 2Sheets-Sheet 1 INVENTOR.

JOEL A. BURTCH,

RNEY

ATT

Aug. 15, 1950 J. A. BURTCH 2,513,361

PHONOGRAPH PICKUP Filed Oct. 30, 1947 2 Sheets-Sheet 2 INVENTOR. JOEL A.BURTCH ATTOR N EY Patented Aug. 15, 1950 UNITED STATES PATENT OFFICEPHONOGRAPH PICKUP Application October 30, 1947, Serial No. 783,114 InGreat Britain March 21, 1947 mounting means other than the semi-solidmaterial.

This invention provides mounting means other than the semi-solidmaterial to facilitate accurate and rapid mass production of thetransducer device shown and described in the aforesaid Lynch applicationand to prevent cold-flow of the semisolid material over a period of timefrom adversely affecting the performance of the transducer device.

In the prior art, transducer elements such as piezoelectric crystalelements for phonograph pickups have been enclosed in semi-solidembedment materials such as petroleum jelly (Vaseline) lanolin and thelike in order to moistureproof the crystal and in order to damp resonantvibrations of the transducer system. These crystal elements werecontained in a housing and the housing was substantially filled with thesemi-solid material. Due to the characteristics of the semi-solidmaterials which had no stifiness and exerted only a mechanicalresistance force against the crystal element throughout its range ofvibration, it could not act as a mounting means and it was necessary tohold the crystal element within the housing by the usual mounting padswhich are well known in the art.

In accordance with this invention there is provided a phonograph pickupcomprising a cupshaped housing having an open end and having a shouldernear its lip which is of smaller diameter than the diameter of the lipof the cup-shaped housing. Planar closure means are provided for theopen end of the housing which engage the shoulder, and its plane extendssubstantially perpendicular to the direction of the axis of the housing.There is a flexing-type piezoelectric crystal element adapted togenerate an electric signal upon being flexed and harness means which isconnected to the closure means supports the crystal element within thehousing. There is a mass of semi-solid material within the housing andin engagement with a substantial area of the crystal element forresiliently resisting the flexing of the element, and driving means areconnected to the element and extend through the housing.

An object of the invention is to provide a new and novel mounting for apiezoelectric transducer element.

Still another object of the invention is to provide a mounting for acrystal element embedded in semi-solid material.

A further object of the invention is to provide new and novel electricalconnections for a crystal element in a phonograph pickup.

Yet another object of the invention is to provide a phonograph pickupwhich is easil assembled.

Other objects and a fuller understanding of the invention may be had byreferring to the following description, claims and drawings wherein:

Fig. l is an isometric view of an assembled pickup; Fig. 2 is a top viewof the pickup; Fig. 3 is a bottom view of the pickup; Fig. 4 is anisometric View, on a larger scale, of a portion of the pickup; Fig. 5 isan isometric view of the crystal assembly used in the pickup; Fig. 6 isa cross-sectional view taken along line 6-6 of Fig. 2; and Fig. '7 is across-sectional view taken along line 'l! of Fig. 6.

In Figures 1, 2 and 3 there is shown a phonograph pickup comprising acup-shaped housing portion 85 having a larger diameter at its lip sothat a shoulder 86 is formed. Against this shoulder there is positioneda base 5! formed of several washers connected together by portions ofthe back end of a stylus guard as. The base 5! substantially closes theend of the cup-shaped housing 85. A harness, shown in detail in Fig. 4,is connected to the base 5| and a piezoelectric crystal element 29 ismounted in the harness for free rotary motion but is restrained from anylateral displacement. A quill 35 is connected to the lower edge of thecrystal element and extends to the outside of the housing 85. A longthin vertically flexible stylus arm carrying a stylus tip 9! isconnected into the quill 35.

As the stylus tip Si is moved laterally by a phonograph record thecrystal element 29 is rotated in its harness.

Within the housing to there is a semi-solid mass of rubber-like material18 contacting a broad area of the crystal and exerting a stifiness forceagainst the crystal I3 as the crystal is twisted by a phonograph recordgroove laterally moving the p f t e S ylus i 6. Because the material I8is compliant and yieldingl tends to hold the crystal in place, a forceapplied to the chuck end of the crystal is stresses the crystal andcauses the crystal to generate an electromotive force representative ofthe mechanical force applied to the crystal. Contrary to the prior art,no mounting pads or other means for forcibly restraining localizedportions of the crystal element is are utilized.

The material !8, when properly chosen in accordance with specificationspresented later, acts as a stillness-controlled mounting for thepiezoelectric crystal element l3 at frequencies below a certainfrequency which varies in accordance with its composition. With thecrystal element vibrating at frequencies up to this certain frequency, aforce potential independent of frequencyis produced across the length ofthe crystal element causing the element to generate a voltage which isalso independent of frequency. At frequencies above this certainfrequency the material is, because of its molecular friction, begins toact as a mechanical resistance to the motion of the crystal element sothat the crystal element now has produced across its length a forcepotential proportional to the frequency of its vibration. Thisgencratesfor a given amplitude of stylus displace ment a voltage output rising ata rate of about 6 db./octave starting at the certain frequency. If themounting material l8 hassomewhat more internal friction the pickupresponse can be made to start rising at a lower frequency, and if it hassomewhat less internal friction the pickup response can be made to startrising at a higher frequency. The point at which the pickup responsestarts to rise may, by analogy to the terms used in the phonograph art,be called the turn-over point. Below the turn over point the forceexerted against the crystal element by the material I3 is predominantlya stillness force althrough there ma also be exerted a mechanicalresistance force. Above the turn-over point the force is predominantly amechanical resistance force although there may also be a stiffness forceexerted.

Commercial phonograph records usually cut constant amplitude to about490 cycles per second and constant velocity above that frequency. Ifsuch a record is reproduced by a phonograph pickup having noequalization an output response fiat to about e cycles second (theturn-over point) is obtained, and the response thereafter falls at arate of about 6 rib/octave. A graph of the output voltage from aphonograph pickup embodying the present invention as the pickupreproduces a commercial phenograph record is hat to about 400 cycles:and falls at a rate of about 6 db./octave between ail-'3 and 700cycles. At this frequency the becomes flat and stays fiat to well outbeyond 7,000 cycles. This provides, without any electri a1 equalization,a base boost which for many applications desirable.

The material It! within the housing is very effectively seals thetransducer element is against moisture. It further provides :a veryeffective shock mount thereby, if it is so d permitting the use of veryfragile, plate crystal elements. In addition to providing an excellentmounting and in addition togproviding internal equalization the materialit also (lamps resonances which may occur in the crystal or in thecrystal system comprising the crystal element l3 and the chuck it.

Satisfactory results from a honogr ph p p of the type shown in Fig. 1are obtained if the material i8 is of the plasticized polyvinyl resintype. One such material is sold under the trade name Korogel.Rubber-like plastic elastomers of the vinylite type are alsosatisfactory. One such elastomer is made b copolymerising polyvinylchloride and. polyvinyl acetate and dispersing the resultant resin in aplasticizer such as dibutyl or dioctal phthalate or a mixture of thetwo.

Many of the materials which are suitable for mounting piezoelectriccrystal elements in accordance with this invention will cold-flow withtime thereby slightly dislodging the crystal eleent. In order to reducethe effects of cold--flow and in order to assemble the pick-up with thecrystal element and its attached stylus assembly accurately in positiona harness, illustrated in Fig. 4, is provided.

The crystal element assembly, indicated generally by the referencecharacter 23, is shown in detail .in Fig. 5. It comprises two plates ofpiezoelectric crystalline material 25 and 26 connected together and tothe leads 2! and 28 to form a multiplate flexing element identifiedgenerally by the reference character 22. The crystal element 29 isprovided at its top with a saddle element 3B of inverted channel formwhich is straddled'across the thickness of the element. At its bottomend the crystal is provided with a cradle element 3!, also of channelform, within which the lower end of the crystal is firmly held. Thecenter portion 32 of the saddle it is raised-slight- 1y above the mainportion, thereof and a pivot 33 extends slightly above the raisedportion The bottom channel 3! carries a pivot point 35.

From the underneath side of the crystal 3! there extends a downwardlyinclined laterally projecting hollow quill 35, the inner end of which issecured to the-cradle 3! by sweating or othersuitable means, and thecradle carries a projection 37 (Fig. 6) which fits into the end of thehollow quill in order to accurately position the quill. The cradle 3!includes an integrally connected locating member 38 which extendsdownwardly from one of its ends. The member 38 has a hole in it throughwhich the quill 35 extends, and. a drop of solder may be applied to thequill at the location where it extends through the member in order tofirmly connect the two together. the quill 35 is firmly connected'toandaccurately aligned with respect to the crystal element Thesub-assembly comprising the crystal element 29 with its connected quill35 is mounted in a frame, or harness, which is shown in Fig. 4. Thecrystal element within the harness is free to rotate but is restrainedagainst movement both lengthwise and laterally to prevent coldflow ofthe semi-solid material from dislodging the crystal element and movingthe stylus out of its position. The mounting frame comprises twoupstanding side portions ill, 6| in the form of flat metal strips havingtheir upper ends 42, 43 inserted through holes 44, 45 in afiat top plate46 which is made of insulation material. The ends 42, 43 of the metalstrips are turned over to connect the top plate 45 to the side legs .8,45. The base of the harness comprises a pair of superimposed flatcircular disks 58, 5! also made of electrical insulation material. Thelower ends 41, 48 of the side legs 40, ll extend downwardly throughslots in the upper base disk 5i! and then turn and extend outwardly inopposite directions within shallow channels 52, 53 provided in one orboth of the'opposing faces of the superimposed base disks 50, 5|. Thelower extremities of the side legs 40, 4| after passing outwardly frombetween the base disks 5!], 5! are turned upwardly to lie substantiallyparallel to the legs M], 4! and these up-turned extremities 55, 56constitute conducting tongues through which electrical connection may bemade to the leads 2?, 28 of the crystal element 23 when the crystalelement is mounted within the harness. The two superimposed base disks5%, 5! are connected together by means of a portion of a fiat stylusguard member 6! which is formed from a spring material. The end of thestylus guard 55 which lies underneath the base 5| is slotted at 6!, 62to provide three tongues 53, 6d, and 55. As may be seen in Fig. 7 theend of each of the tongues 63, 65 is slotted for a short distance at 65to form two tabs 51, 61' at the end of each of the tongues '63, 65.longues 6B, 55 extend upwardly through registering slots 58, $8 in thebase disks 5%, 5i and the two tab portions Bl, ill of each of thetongues are folded over in opposite directions against the upper face ofthe disk lit! to clamp the two disk portions 58, El together therebyfirmly holding legs 45, l! place. The central tongue portion 84 of thestylus guard {55 is bent upwardly to form an upstanding portion is andis then again bent to form a horizontal portion 3' l. The horizontalportion H has a small detent l2 in it and the top plate it has a smalldetent is (shown in Fig. 7) located near its center. The crystalassembly shown in Fig. 5 fits into the harness shown in Fig. 4 with thesaddle 3% extending substantially perpendicular to the direction of thetop plate 46 of the harness. The pivot point 33 fits into the detent l3,and the pivot point as fits into the detent 12. Due to the springinessof the stylus guard til, the tongue portion 54 biases the crystalassembly upwardly against the top plate 46 thereby resiliently holdingthe crystal sub-assembly in place. It is preferable to resiliently holdthe crystal assembly in place by means of a spring urging the crystalassembly upwards against a stiir top member rather than by a springurging the crystal assembly downwardly against a stiff base as a suddenblow on the stylus arm, such as by dropping the pickup arm onto thestylus will not dislodge the pivot points from the pivots when theformer construction is used. The crystal lead Z'l is wound around themetal leg ll and soldered to it, and crystal lead 28 is wound around andsoldered to the metal leg A li, as shown in Fig. '2. The quill 35 of thecrystal sub-assembly extends in a direction toward the outer end of thestylus guard 58 which is bifurcated to establish two leg portions and 82with a notch there etween. Each of the legs at its outer end is dimpledto establish on its lower face a smooth bearing surface 82, 83 and, asis shown best in Fig. 6, each leg is arched upwardly from the mainportion of the stylus guard A cannister, or housing, 85 which is deeplycup-shaped is provided. This cannister 35 is filled with semi-solidcrystal-supporting material l8 and th crystal sub assernbly comprisingthe crystal assembly 23 mounted in its harness is positioned in thecannister with the upper disk 5d of the base engaging a narrowedshoulder 86 of the cannister and closing the open end of the cannister.

The cannister 85 is adapted to be connected to a phonograph pickup arm,so in order to assure true alignment of the stylus arm with respect tothe pickup arm the stylus arm must be accurately aligned with respect tothe cannister. The crystal assembly, including the quill 35, is mountedin the frame and a stylus assembly Si] is connected into the quill 35.The deeply cup-shaped cannister is filled with liquid material which,when processed, becomes semi-solid. While the material is is in a liquidstate the crystal assembly, in its frame, is pushed into the filledcannister until the upper disk 58 of the base engages a narrowedshoulder 86 of the cannister. This accurately places the frame withrespect to the cannister 85. The stylus assembly is firmly held in thenotch S t in the stylus guard thus orienting the crystal 2% with respectto the frame and the stylus with respect to the cannister while thematerial l8 solidifies. The cannister 85 is notched at three places ill,88 and 89 around its lip, and the extremity 55 of the metal leg 40extends outwardly from the cannister 85 through slot 81. When thecrystal assembly is in place in the cannister 85 the top surface of theleg extremity 55 engages the can" nister 85, thereby making anelectrical contact. This is the ground side of the electrical circuit tothe piezoelectric crystal 29 and the cannister 85 thereby becomes agrounded electrical shield. The leg extremity 56 extends outwardly fromthe cannister 85 through the slot 89, but is spaced from the cannisterto prevent electrical contact and the quill 35 extends outwardly fromthe cannister 85 through the slot 88.

The stylus assembly is easily replaceable. It comprises a long, thinstrip of metal 96 into one end of which is connected a jewel stylus tip9!. The end of the stylus arm 90 opposite the stylus tip 9! is bentslightly as at 92 so that as the stylus arm is pushed into the hollowquill 35 the bend in the arm is flattened to cause it to firmly engagethe walls of the quill. This holds the stylus arm into the quill byfriction alone, obviating the use of thumb screws and the like andgreatly reducing the mass of the stylus assembly. By so mounting thestylus arm in the quill 35 it may easily be replaced. A pull on thestylus arm in a direction substantially parallel to the direction ofextension of the quill 35 easily removes the stylus arm from the quilland to replace it with a new one, the new stylus arm is merely pushedback into the quill. The stylus is arched slightly at 83, and when thestylus arm is in place in the quill 35 with the stylus tip 9! lyingbetween the legs at, st of the stylus guard 68, the stylus tip 9!projects just slightly below the bearings 82, 83. As is shown in Fig. 6the arched portion of the stylus arm 99 is located substantially at thepoint where the stylus arm extends between the legs 3B, 8! of the stylusguard Bil. When the pickup is not in engagement with the record thestylus arm 52 rests in the notch 95 between the legs 8! thereby holdingthe stylus arm and preventing cold-flow of material l8 over a period oftime from dislodging the stylus. When the pickup is bein used totranscribe a record, the operator lowers the pickup arm supporting thecannister 35 until the stylus tip 9| engages the record 96 and supportsthe unbalanced weight of the pickup arm. This unbalanced weight liftsthe stylus arm 98 slightly with respect to the stylus guard 5d, therebyreleasing the stylus arm till from the notch 94 so that the arm can movelaterally a limited distance under the influence of the grooves in thephonograph record 96. When the pickup is lifted from the record thestylus arm 9:) once more is locked by the notch 95. If the stylus arm iscarelessly dropped onto the record the stylus arm .90 bends readilyuntil the smooth bearings 32, 3.3 at the extremity of the stylus guardto hit the record .96. The spring guard 68 is much stiiferzthanthespring'pickup arm and it easily absorbs the force of dropping the pickuparm without damage to'itself, and, due to the large area of the bearings82, 83 compared to the small area in the tip of a phonograph stylus, therecord is not damaged by the guard. The greater vertical flexibility ofthe stylus arm allows the stylus ill to retract under the force of thefall thus preventing damage to the record by the stylus tip.

This stylus construction eliminates the usual stylus chuckwith itsclamping screws. It eliminates soldering operations during the replacingof the stylus and, most important of all, it greatly reduces the stylusassembly weight and consequently the dynamic inertia forcesinvolved-when a record is reproduced. The stylus arm assembly weighsapproximately .0015 ounce.

In order that the crystal element 23 shall move freely under theinfluence of driving forces from the stylus system it is important thatshear forces in the mounting material it be kept to a minimum. Theseshear forces exist in the semisolid material between the crystal .saddle3i! and the top cross-bar '46 of the frame and b tween the crystalcradle Si and the top surface of the base disk 59. In order to reducethe shear force at the top of the crystal element to prevent locking ofthe top .edge of the movable crystal element to the stationary frame,the saddle '36 is provided with a step 32 between the pivot 33 and thetop surface of the saddle. This step 32 spaces the main portion of thesaddle sufficiently far away from the cross-bar 46 of the frame that anappreciable depth of the semi-solid material will exist between thesaddle and the cross-bar. Because of the appreciable depth of thesemisolid material the shear forces produced therein by motion of thecrystal element with respect to the harness is kept to a minimum valuewhich does not disturb the operation of the device. The lower edge ofthecrystal element 2'9 moves with greater amplitude than the upper edge soit is of even greater importance that high shear forces be prevented inthe material l8 which lies between the lower edge of the crystal element29 and the top face of the base disk Ell. This is achieved by providingregistering slots I in the base disks 55, to accommodate the quill 35which extends downwardly and outwardly from the center portion of thelower edge of the crystal element 29. The semi-solid material !8 coversthe lower edge of the crystal element 29, as is shown in Fig. 6, andfills the quill slot Hid thereby damping the vibrations of the quill,and because of the relatively large amount ofsemi-solid material 18keeping the shear forces low. In the top surface of the base disk '56immediately below the back corner 29' of the crystal element 25 there isprovided a groove ltl which is'filled with semi-solid material IS. Thedepth of the material is between the cradle 3i and the bottom of thegroove It! is sufiicient to prevent high shear forces in the materialI8.

From 6 it will be noted that the lower pivot point 3c is not on thevertical center line of the crystal element but is set back a shortdistance toward the back corner 2?? of the crystal element. If thecrystal element were suspended in the semi-solid mounting material l3without a harness, lowfrequency vibrations would cause it to vibrateabout a line running from somewhere in the vicinity of the lower-backcorner 29' of 8 thecrystal plate up toward-the central portionof the topedge of the crystal plate. As the crystal element vibrated at'higherfrequencies thelower pivot point would move in toward the verticalcenter line of the crystal element.

While there have been described what areat present considered to he thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is,therefore,zaimed-in the appended claims to cover all such changes andmodificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A phonograph pickup --comprising, a cupshaped housing having a-nopenend and having a shoulder near the lip thereof which is of smallerdiameter than the diameter of the lip of :said cup-shaped housing,planar closure means for the open end of said housing engaging .saidshoulder with the plane of said closure meansextending substantiallyperpendicular to thElfliI'fiC- tion of the axis of said'housing, aflexing type electromechanical transducer element, harness means mountedon said closure means and positioned within said housing and"connected'to .said transducer element for supporting said transducerelement within said housing, a mass of semi-solid material havingstiffness less thanzthe stiffness of said transducer element'within saidhousing and in engagement with substahtially'the entire area of saidtransducer element for resiliently resisting the flexing of saidelement, and driving means connected to saidelement and eX tendingthrough said housing for flexing said transducer element.

2. A phonograph pickup as set forth inclaim 1, further characterized bysaid harness means comprising two legs connected to and upstanding fromsaid closure'meana'said legs being electrically conductiveand'insulated'from each other by said closure means, and twoelectricalleads each of which is connected to said transducer elementand to one of the said legs ofsaid harness.

3. A phonograph pickup as set forth inelaim 2, further characterized bymeans connecting one end of each of said two legs to saidclosure means,a cross-bar insuiatedly interconnecting the other ends of said twoupstanding legs, and pivot'means carried by said cross-bar and by saidclosure means for pivotably supporting said transducer element.

A phonograph pickup as set forth in claim 1, wherein said driving meansincludes a stylus, further characterized by said closure meanscomprising two plates each having a slot therethrough superposed inface-to-facerelationship with the said slots in registration, and'byguard means one'end of which protects said stylus and the other end ofwhich extends through said registering slots in said two superposedplates and is bent over an angle to secure said two plates together.

5. A phonograph pickup as set forth in-claim 4, further characterized bya first and a second channel extending between said two plates from theedge of said closure means toward the center thereof, the upper of saidtwo plates having first and second slots through it each of whichcommunicates one of said channels at its inner end, said harness meansincluding two spaced-apart legs each of which is connected to saidclosure means by one end thereof extending down through one of said twoslots in said upper plate and out through said channel between said twoplates.

6. A phonograph pickup as set forth in claim 5, further characterized bysaid two harness legs extending from said two channels out beyond theedge of said closure means forming electric terminals for said pickup.

7. A phonograph pickup comprising, a base member, a frame having twoupstanding electrically conductive legs connected to and extending awayfrom the base member and a crossbar connected between and insulated fromsaid legs, a flexing type elec romechanical transducer element havingtwo electrical leads, pivot means pivotally supporting said transducerelement between said base member and said frame for substantially freepivotal motion, each of said leads being electrically connected to oneof said legs, housing means enclosing said frame and said transducerelement, two terminals extending through said housing means andelectrically connected, respectively, to said two legs, driving meansconnected to said transducer element and extending to the outside ofsaid housing, and means Within said housing and in engagement with saidtransducer element for resiliently resisting the flexing of saidtransducer element.

8. A phonograph pickup comprising, a flexing type transducer elementhaving two leads, a housing including a cup-shaped portion and a 10closure portion of insulating material secured to the open end thereof;harness means secured to said closure portion and comprising a pair ofspaced-apart electrically conductive legs one end of each of which isconnected to said closure portion; said legs extending into saidcup-shaped portion, and a cross-bar of insulating material secured tothe other end of each of said legs; means pivotably securing saidtransducer element between said closure portion and said cross-bar, eachof said transducer element leads being electrically connected to one ofsaid legs, and terminal means connected to each of said legs and extending outside of said housing for connection in an electric circuit.

JOEL A. BUR'ICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 20,680 Sawyer Mar. 29, 19381,827,919 Van Wagenen Oct. 20, 1931 2,208,940 Dunning July 23, 19402,313,129 Dohan Mar. 4, 1943 2,363,493 Begun Nov. 28, 1944 2,363,497Begun Nov. 28, 1944

